Nonwoven fabrics and laminates have many applications in the medical and hygienic field. For example, nonwoven laminates may be constructed for applications such as surgical caps, gowns or patient drapes, medical table covers, isolation gowns, scrub apparel or for other protective apparel, among others. In these applications, it is desirable to have a nonwoven laminate product that not only provides comfort (i.e., softness) and good ability to drape as desired (i.e., flexibility), but is also capable of withstanding both processing and in-use conditions. In particular, a nonwoven laminate product sufficient for medical applications should: (i) provide blood, bacteria and viral barrier properties; (ii) be absorbent or repellent (depending on end-use application); and (iii) maintain its integrity (i.e., it should not delaminate) in a wet state, for example, after soaking in bodily fluids such as sweat, urine or blood.
Before use in a medical application, such nonwoven laminates are typically wound on a roll and shipped to a manufacturer, who converts the laminate into the end product, sterilizes the end product using steam, gamma radiation or EtO sterilization, and places the sterilized end product into a plastic pouch. Therefore, it is also desirable for such nonwoven laminates to be constructed to withstand the handling, aging and sterilization required for nonwoven products having medical application without degradation.
To achieve the foregoing properties, many products have been developed comprising multiple thermally bonded nonwoven layers. For example, U.S. Pat. No. 4,695,334 to Mays, which is hereby incorporated by reference, discloses a multiple layer plastic film that is fused or thermally bonded to at least one layer of conjugate fibers having a low melting sheath and a high melting core. The sheaths of the conjugate fibers are fuse bonded to the plastic film at a temperature below the melt temperature of the cores of the conjugate fibers so that the cores retain their initial fiber-like integrity. Other commercially available products utilize alternative methods for bonding a plastic film layer to a fiber layer, such as ultrasonic bonding, adhesive bonding, or thermal spot bonding. It is also known that the Corona treatment improves a fabric's dry peel strength (Butler, T. I. and Veazy, E. W., Film Extrusion Manual: Process, Materials, Properties, 1992, TAPPI Press, Atlanta, pages 363-416).
It has been found, however, that some products exhibit substantially reduced wet peel strengths after aging and EtO sterilization. This may result from migration of adhesive from the interface between the film and fiber layers to the fiber layers when the nonwoven is in roll form, or from the temperature and humidity used during EtO sterilization. The present invention seeks to overcome these problems by producing a low cost nonwoven laminate product comprising a novel co-extruded film adhesively bonded to a spunbond or other nonwoven substrate.